The purpose of this study is to identify those factors which control transovarial transmission of arboviruses by mosquitoes. Results to date indicate that a number of flaviviruses (Japanese encephalitis, yellow fever, dengue, Kunjin, Kokobera, Uganda-S, Ilheus, Banzi and Bussuquara) as well as two bunya-viruses (Keystone and San Angelo) can be transovarially transmitted by experimentally infected Aedes mosquitoes. In addition, differences were observed among several geographic strains of Aedes albopictus in their efficiency of vertical transmission of Kunjin virus. Different strains of Kunjin virus also varied in their ability to be transovarially transmitted in mosquitoes. These studies suggest that vertical transmission of arboviruses by mosquitoes may be an alternative mechanism for biological survival of the viruses.